Electronic devices such as diodes, transistors and the like are commonly used in many items found in homes, offices, vehicles, personal electronics, communications, computers, industrial and aerospace applications, medical devices and elsewhere. Generally speaking, a transistor is a three-terminal device that provides signal routing, amplification, and switching capabilities in analog and digital circuits. Recently, efforts have been focused upon creating transistors that perform various functions with reduced power consumption. The ability to reduce power consumption is particularly desirable in battery powered applications, such as cell phones, laptops, portable audio and video equipment, digital watches, pocket calculators, wireless pagers, and medical implants including pacemakers, artificial cochlea, and the like. Low-power applications are typically implemented using ultra-large-scale-integration (ULSI) circuits, which frequently require low power devices to minimize total power dissipation.
Micropower circuits based on sub-threshold transistor operation are widely used in the aforementioned low-power applications. The majority of these micropower circuits have been fabricated using standard CMOS processing. The micropower operation is achieved by ensuring that most of the MOSFETs are biased in the sub-threshold regime, commonly known as weak-inversion. The drain current flowing in a weakly inverted MOSFET is typically in the range 10−10 to 10−5 amps per micron of channel width. The low current, combined with the low drain voltage required to achieve current saturation (Vdsat>3kT/e˜75 mV) is one reason for the low power consumed by micropower CMOS circuits. Since the cut-off frequency of a weakly inverted MOSFET is very low, micropower CMOS circuits typically operate at frequencies less than 10 MHz.